1. Field
The present teachings relate to performance mismatch detection in RF circuits, including performance compensation using such mismatch detection. More particularly, the present teachings relate to performance mismatch detection using a replica circuit, where one or more operating variables of the replica circuit that affect performance are made to be intentionally different from operating variables of a main circuit.
2. Description of Related Art
Performance of an RF circuit can be based on a set of operating characteristics of the RF circuit. Such operating characteristics may comprise a signal modulation characteristic, a signal linearity characteristic, a signal distortion characteristic, a signal magnitude characteristic, a signal phase characteristic, a transient response characteristic, a temperature characteristic, and other characteristics used as metrics to a performance of the RF circuit. During operation of the RF circuit, such operating characteristics may be affected by operating variables to which the RF circuit is subjected. In turn, the operating variables can cause performance of the RF circuit to deviate from a nominal performance. Such operating variables may comprise a load to the RF circuit, a local temperature at the RF circuit, HCI and floating body effects of transistor devices of the RF circuit, transient effects associated to transition from idle/inactive to normal/active modes of operation of the RF circuit, different operating modes of the RF circuit, different frequencies of operation of the RF circuit, etc.
In some cases, it may not be desirable to directly measure performance of the RF circuit during normal operation of the RF circuit, since coupling to the RF circuit for the sake of the measurement may adversely affect performance of the RF circuit. One may consider measuring the performance during a test mode of the RF circuit with the drawback of not being able to compensate in real time (during normal operation). In other cases, performance, per the operating characteristics, may not be directly measured, but rather derived by way of signals sensed from the RF circuit. Such signals may be influenced by the operating variables in such way that they may not be representative of the real performance of the RF circuit.
A varying load coupled to an output node of the RF circuit can affect a VSWR of the circuit. Such varying load may be caused by a varying antenna, or elements coupled to the output node affected by various operating variables. VSWR (voltage standing wave ratio) is a metric commonly used to indicate a degree of impedance mismatch between two different stages in a circuit (e.g. a power amplifier and a transmitting antenna). A VSWR of 1:1 indicates a perfect impedance match (e.g. no reflected wave) while higher measures of VSWR indicate higher degrees of impedance mismatch (e.g. a VSWR of 10:1 indicates higher impedance mismatch than a VSWR of 5:1). In prior art embodiments, measurement of VSWR can be performed using a dual directional coupler and a complete power detector in order to measure both forward and reflected waves from which the VSWR measurement can be derived.
For example, an impedance mismatch between two stages of a circuit such as a power amplifier and a transmitting antenna can occur because antenna impedance can be influenced by a surrounding environment of the transmitting antenna. By way of example, and not of limitation, at assembly time the antenna may have a particular surrounding environment, leading to a first value of antenna impedance. The power amplifier may be matched to the first value of the antenna impedance. If the environment surrounding the antenna changes, antenna impedance may change to a second value as a result of the environmental change. As one example, placing the transmitting antenna on a metal table can alter the antenna impedance, causing an impedance mismatch between the power amplifier and the transmitting antenna. As another example, metal objects in proximity to the transmitting antenna can affect the antenna impedance.